Formidable

внуши́тельный

vnušítelʹnyj

(causing fear, dread, awe or admiration as a result of size, strength, or some other impressive quality)

гро́зный

gróznyj

(causing fear, dread, awe or admiration as a result of size, strength, or some other impressive quality)

труднопреодоли́мый

trudnopreodolímyj

(difficult to defeat or overcome)

трудноразреши́мый

trudnorazrešímyj

(difficult to defeat or overcome)

устраша́ющий

ustrašájuščij

(causing fear, dread, awe or admiration as a result of size, strength, or some other impressive quality)

чудо́вищный

čudóviščnyj

(causing fear, dread, awe or admiration as a result of size, strength, or some other impressive quality)